Bianca Rinehart, daughter of mining billionaire Gina Rinehart, has been threatened and intimidated by her mother since a feud over a family trust began, a Sydney court has heard.

Ms Rinehart has faced Sydney's Supreme Court to argue why she should be allowed to take control of a $5 billion family trust.

Mrs Rinehart stepped aside as trustee in late 2013 and a civil case is trying to determine whether a family member or an outsider should take her place.

Before the magnate stepped aside, three of her children - John Hancock, Bianca Rinehart and Hope Welker - accused her of misconduct by changing the date they could access their trust money without telling them.

Ms Welker has since pulled out of the case after reaching a private agreement with her mother.

Bianca Rinehart is the first family member to give evidence in court since the case was lodged three years ago.

The Supreme Court heard Bianca had the best interests of the beneficiaries at heart and had the support of her brother, Mr Hancock, for the role.

Under questioning from a lawyer for the youngest Rinehart child, Ginia, who is siding with her mother in the dispute, Ms Rinehart admitted she may have in the past referred to Mr Hancock as an idiot.

However, she qualified the remark by saying she did not always agree with everything Mr Hancock said.

Ms Rinehart struggled to recall if she had told her mother that Mr Hancock had a desire for money and fame.

She also also admitted Mr Hancock had called Ginia a moron, an oxygen thief and intellectually disabled.

She said she did not personally approve of the language, but that Mr Hancock probably made the comments because he did not want someone running the trust who was not up to it.

Rinehart asked Grant Hackett to intervene in feud, court hears

The court heard that at one point Gina Rinehart emailed Olympic swimmer and family friend Grant Hackett to ask him to intervene in the feud.

Bianca Rinehart admitted to the court that she had changed her mind several times about nominating herself as trustee over the past few years, but said she was now committed to taking on the role.

She said she would feel "empowered" to run the trust, despite the stress it might bring.

"I'm here today and I'm prepared to act as trustee," she said.

Lineal Hancock descendent 'must control the trust'

Ms Rinehart's barrister, Christopher Withers, argued that under an arrangement between the family company Hancock Prospecting and mining giant Rio Tinto, a lineal descendent must control the trust.

Ms Rinehart is a lineal descendent, he said.

Mr Withers said the threats and intimidation Ms Rinehart had withstood from her mother showed she had "the strength of character " required for the job.

Both Ginia and Gina Rinehart want an independent trustee to be appointed.